1. Field of the Invention
The present invention relates to a novel gene encoding a malic enzyme and a method for preparing succinic acid using the same, more particularly, to a maeB gene encoding a malic enzyme B having the activity of converting pyruvic acid or pyruvate to malic acid or malate, or vice versa, a recombinant vector containing the gene, a microorganism transformed with the recombinant vector, and a method for preparing succinic acid using the transformed microorganism.
2. Background of the Related Art
Succinic acid, which is a dicarboxylic acid (HOOCCH2CH2COOH) with four carbon atoms initially purified from amber resin, is used in a very wide range of industrial applications (Zeikus et al., Appl. Microbiol. Biotechnol., 51:545, 1999). Particularly, as the utility of succinic acid as a main raw material of biodegradable polymers was recently proven, a rapid increase in the demand of succinic acid is expected (Willke et al., Appl. Microbiol. Biotechnol., 66:131, 2004).
Succinic acid can be produced by chemical synthesis and fermentation. Most commercially available succinic acid recently has been produced from n-butane as a starting material derived from LNG or crude petroleum, by chemical manufacturers, such as BASF, DuPont and BP Chemicals. Chemical processes for the synthesis of succinic acid have the problem that they cause the discharge of large amounts of harmful solid wastes, waste solutions and waste gases (including carbon monoxide) during the preparation of succinic acid, and particularly, have the limitation that they use fossil raw material as a basic material. Only a small amount of succinic acid, which is used in special applications, such as medical drugs, is currently produced by traditional microbial processes.
In an attempt to solve the described problems occurring in the chemical processes for the synthesis of succinic acid, studies on the production of succinic acid by fermentation processes have been conducted by many researchers. The method for the production of succinic acid by fermentation is a method of producing succinic acid from renewable raw materials using microorganisms. Bacterial strains which are used in the production of succinic acid can be broadly divided into recombinant E. coli and ruminal bacteria, such as Actinobacillus, Anaerobiospirillum, Bacteroides, Mannheimia, Succinimonas, Succinivibrio, etc.
A research team of the University of Chicago has attempted to increase the production of succinic acid by preparing a mutant strain AFP111 (ATCC No. 202021) in which E. coli ldh and pfl genes involved in the production of lactic acid and formic acid have been removed and a ptsG gene of the glucose transfer system has been manipulated (U.S. Pat. No. 5,770,435).
Among ruminal bacteria, Actinobacillus, Anaerobiospirillum and Mannheimia strains have been relatively much-studied. Michigan Biotechnology Institute (MBI) has developed an Actinobacillus succinogenes 130Z strain (ATCC No. 55618) and a process for producing a high concentration of succinic acid using the same (U.S. Pat. No. 5,504,004). Also, such institute has developed Anaerobiospirillum succiniciproducens and its mutant strains, and a process for the production and purification of succinic acid (U.S. Pat. Nos. 5,521,075; 5,168,055; and 5,143,834).
However, the processes for preparing succinic acid using the described strains have low productivity and result in the production of large amounts of byproducts in addition to succinic acid, thus requiring high costs for the separation and purification of succinic acid. Accordingly, there has been an urgent need for the development of a bacterial system that has high productivity and at the same time, can inhibit the production of byproducts (Hong et al., Biotechnol. Lett., 22:871, 2000).
For this purpose, the isolation of an excellent succinic acid-producing bacterial strain, the establishment of genome sequences and the understanding of metabolic characteristics of bacterial strains based on them are first required. With such basis, it then is necessary to secure gene manipulation technologies required for the construction of a novel gene recombinant bacterial strain. Although there has been a prior attempt to increase the production of succinic acid using the phosphoenolpyruvate carboxykinase (pckA) gene of Anaerobiospirillum succiniciproducens (Laivenieks et al., Appl. Environ. Microbiol., 63:2273, 1997), the art has failed to develop a gene recombinant strain based on the full genome sequence of ruminal bacteria.
Meanwhile, the present inventors previously isolated a Mannheimia succiniciproducens MBEL55E strain from the rumen of a Korean cow that produces succinic acid in high efficiency using various substrates, and reported the full genome sequence of the strain (Hong et al., Nature Biotechnol., 22:1275, 2004). Particularly, the above strain is characterized by immobilizing carbon dioxide, known as a greenhouse gas, in the synthesis of succinic acid. Also, this applicant previously prepared succinic acid with high yield by deleting a lactic acid dehydrogenase gene (ldhA) and a pyruvate formate-lyase (pfl) from Mannheimia succiniciproducens MBEL55E, so as to construct mutant strain Mannheimia sp. LPK (KCTC 10558BP), and deleting a phosphotransacetylase gene (pta) and an acetate kinase gene (ackA) from the LPK strain to construct mutant strains Mannheimia sp. LPK7, and then culturing the resulting mutant strain in an anaerobic condition (WO 05/052135 A1). However, the mutant strain has a problem that it results in the accumulation of malate to a certain degree as a byproduct during the culture thereof.
Accordingly, there continues to be an urgent need in the art for the development of a bacterial system for high productivity, low byproduct succinic acid production that overcomes the deficiencies of the prior art